Local residents bring flowers to place them on armoured personnel carriers in Slaviansk.

Reuters/ Gleb Garanich

Armoured personnel carriers (APCs) operated by Ukrainian armed forces are now believed to be in the control of pro-Russian separatists after Ukrainian soldiers surrendered their vehicles.

Amid escalating rhetoric between Moscow and Kiev, the incident highlighted defiance by pro-Russian separatists, undermining central government efforts to push armed rebels out of captured buildings in 10 eastern towns without bloodshed.

Ukrainian troops had driven the APCs, flying the Ukrainian flag, into the town of Kramatorsk after securing control of a nearby airfield from the rebels on Tuesday, prompting Russian president Vladimir Putin to warn of the risk of civil war.

But the APCs were later seen under the control of pro-Russian separatists in the centre of Slaviansk.

The vehicles then rumbled into Slaviansk, just 15km away, with Russian and separatist flags and armed men in motley combat fatigues on top.

They stopped outside the town hall, which is occupied by separatists.

As they drove in waving, some people waved back and shouted: "Well done lads!" and "Russia, Russia!"

Overhead, a Ukrainian jet fighter carried out several minutes of aerobatics above the town's main square in a show of strength by Kiev's forces.

All the soldiers and the officers are here. We are all boys who won't shoot our own people.

Unidentified Ukraine soldier, member of the 25th paratrooper division.

A soldier, who told told journalists in Kramatorsk he was a member of Ukraine's 25th paratrooper division from Dnipropetrovsk, that he and his fellow troops had not been fed on their own base for three days.

"All the soldiers and the officers are here. We are all boys who won't shoot our own people," said the soldier, whose uniform did not have any identifying markings on it.

"They're feeding us here. Who do you think we are going to fight for?"

"At the start there was information that the armoured personnel carriers entered the town within the framework of the counter-terrorist operation, but their subsequent fate... " Mr Yarema said without finishing his sentence.

Meanwhile, NATO said it had decided on a series of immediate steps to reinforce its forces in eastern Europe because of the Ukraine crisis.

"You will see deployments at sea, in the air, on land to take place immediately, that means within days," NATO secretary-general Anders Fogh Rasmussen said.

NATO fighter aircraft will fly more sorties over the Baltic region, allied ships will deploy to the Baltic sea, the eastern Mediterranean and elsewhere, and allied military staff will be sent out to improve NATO's preparedness, training and exercises.